Covers for electrical and mechanical apparatus typically comprise dust and dirt covers which are made of materials that are impervious to moisture and dust, such as vinyl sheet. While effective, these covers also tend to be restrictive to air flow so that the covers must be removed prior to operating the apparatus, especially electrical apparatus which have openings for cooling. In apparatus such as computers and the like, fans are enclosed within the housing for circulating cooling air over the interior electrical devices which may heat up during operation. The housing also includes louvers through which the fan forces cooling air to flow. It is important in these structures to permit air to flow freely when in use, and thus, the air restrictive dust covers must be removed during operation of the apparatus. Further, such covers tend to enclose the entire apparatus, mandating removal prior to operating the system to permit access to areas such as the keyboard, disc slots and the monitor.
Thus one or more of the housing openings of an electrical apparatus, such as a computer, need to be exposed to the ambient atmosphere during operation of the apparatus. Some of the openings must be exposed to the ambient atmosphere without filtering, for example, the keyboard. However, a need is seen for a dust filter that can be used while a computer system is in operation and that will provide a filtering action against dust particles in the ambient air that can injure delicate and complex parts of the system, such as printed circuit boards and the like.